1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and, more particularly, a semiconductor device manufacturing method having a capacitor.
2. Description of the Prior Art
As the nonvolatile memory that can store information after the power supply is turned OFF, the flash memory or the ferroelectric memory (FeRAM) has been known.
The flash memory has the floating gate buried in the gate insulating film of the insulated-gate field effect transistor (IGFET), and stores information by accumulating the charge as stored information in the floating gate. The tunnel current must be passed through the gate insulating film to write/erase the information. Thus, the relatively high voltage is needed.
The FeRAM has the ferroelectric capacitor that stores the information by utilizing the hysteresis characteristic of the ferroelectric substance. In the ferroelectric capacitor, the ferroelectric film formed between the upper electrode and the lower electrode generates the polarization in response to the voltage value applied between the upper electrode and the lower electrode, and has the spontaneous polarization that holds the polarization after the applied voltage is removed. When the polarity of the applied voltage is inverted, the polarity of the spontaneous polarization is also inverted. The information can be read by detecting the polarity and the magnitude of the spontaneous polarization.
FeRAM has such an advantages that it can operate at the lower voltage than the flash memory and the high-speed loading can be achieved while saving a power.
The planar ferroelectric capacitor employed in the memory cell of the FeRAM is formed by steps shown in FIGS. 1A to 1C, for example.
First, as shown in FIG. 1A, a first metal film 103, a ferroelectric film 104, and a second metal film 105 are formed on a first interlayer insulating film 102 that covers a silicon substrate 101. Then, as shown in FIG. 1B, an upper electrode 105a of a capacitor Qo is formed by patterning the second metal film 105, and then a dielectric film 104a of the capacitor Qo is formed by patterning the ferroelectric film 104. Then, a lower electrode 103a of the capacitor Qo is formed by patterning the first metal film 103. Then, as shown in FIG. 1C, the capacitor Qo is covered with a second interlayer insulating film 106 made of silicon oxide. Then, a first hole 106a is formed on the lower electrode 103a, and then a conductive plug 107 is formed in the first hole 106a. Then, a second hole 106b is formed on the upper electrode 105a. Then, a first wiring 108a, which is connected to the upper electrode 105a via the second hole 106b, and a second wiring 108b, which is connected to the conductive plug 107, are formed on the second interlayer insulating film 106 respectively.
As the material of the ferroelectric film 104 constituting the capacitor Qo, normally ferroelectric oxide such as PZT is employed.
By the way, if the reducing substance is present around the ferroelectric film, there is such a possibility that writing/reading of the ferroelectric capacitor cannot be executed since the polarization characteristic of the ferroelectric film is deteriorated. Therefore, in the above steps, moisture, hydrogen, etc. in the interlayer insulating films 102, 106 cause the ferroelectric film 104 (104a) to deteriorate.
For such problem, as set forth in Patent Application Publication (KOKAI) 2001-60669, Patent Application Publication (KOKAI) 2002-9256, Patent Application Publication (KOKAI) 2002-94021, etc., for example, dehydration or reforming of the interlayer insulating film is executed by exposing such interlayer insulating film to the atmosphere in which N2O, N2 or NO is plasmanized.
However, in order to improve the electric characteristics of the ferroelectric capacitor much more, desorption of moisture from the interlayer insulating film to the ferroelectric capacitor must be prevented as much as possible.